Plastic lenses are lightweight, has excellent moldability, processability, dyeing affinity and the like, and has high safety because of being hard to break, as compared with glass lenses, and therefore are rapidly spreading in the field of eyeglass lenses. Recently, high refractive index materials such as thiourethane resins or episulfide resins are developed in order to answer further requirements of thin and lightweight eyeglass lenses.
On the other hand, plastic lenses are liable to be scratched, as compared with glass lenses. Therefore, it is generally carried out that a hard coat layer is formed on a surface of a plastic lens to improve surface hardness. Further, an antireflective layer is formed on the surface of the hard coat layer by depositing an inorganic substance thereon for the purpose of preventing surface reflection, and an antifouling layer comprising an organosilicon compound containing fluorine is further formed on the surface of the antireflective layer for the purpose of improving water-repellent and oil-repellent properties of the surface. Thus, the plastic lenses are further extending as an advanced lens by virtue of technical innovation of surface treatment.
On the other hand, a plastic lens having both a hard coat layer and an antireflective layer formed thereon has the disadvantage that its impact resistance markedly deteriorates. Some means are proposed on the approach to improve impact resistance of such a plastic lens.
For example, a technique of using a primer composition comprising an ester-based thermoplastic elastomer as a main component to improve impact resistance is proposed as described in, for example, JP-A-11-310755. However, this primer composition has a property that it is difficult to obtain adhesion to particularly a hard coat formed on a surface of a primer layer, and thus had the problem on durability. In addition, impact resistance is improved by the primer layer, but it is not yet reached to a level satisfied on practical use.
Apart from the above, plastic lenses generally have the problem of low heat resistance. With increasing refractive index of plastic lens resin materials, heat resistance of the resin material itself tends to decrease. Due to this tendency, an inorganic antireflective layer formed on an upper layer cannot follow thermal expansion deformation of a plastic lens, and as a result, there is the problem of causing fog or cracks. The problem tends to be remarkable with increasing refractive index of a plastic lens.
Against such a problem, when an antireflective layer comprising an organic thin film is formed on a plastic lens substrate, the layer can follow thermal expansion deformation of the plastic lens substrate, thereby heat resistance can be improved. However, the antireflective layer comprising an organic thin film has relatively large porosity as compared with an inorganic antireflective layer, and cannot substantially be expected to have properties (protecting effect) of shielding factors that deteriorate durability of a plastic lens, such as oxygen, moisture and ultraviolet light, from the outside of the lens. As a result, heat resistance is improved as compared with the case of using an inorganic antireflective layer, but durability tends to deteriorate.
To improve the durability, an approach of improving durability of a hard coat layer itself formed on a lower layer, or an approach of interposing a primer layer between a hard coat layer and a plastic substrate to improve adhesion therebetween is considered.
A technique of forming a hard coat layer using a coating composition containing metal oxide fine particles comprising as a main component, titanium oxide having a rutile crystal structure is proposed as the former. The hard coat layer uses low photoactive titanium oxide. Consequently, durability is improved, and high refractive index can be maintained, as compared with the conventional titanium oxide having an anatase crystal structure, as described in, for example, JP-A-11-310755.
The latter is a technique having both the effect of improving adhesion and the effect of improving impact resistance, by using a primer layer as same as in a surface modification technique such as saponification or etching by plasma irradiation, as described in, for example, JP-A-2000-144048.
However, plastic lenses having an antireflective layer comprising an organic thin film had the problem that where a hard coat and a primer technique are combined, it is difficult to obtain adhesion between the primer layer and the hard coat layer, and durability deteriorates. Further, although impact resistance is improved to a certain extent, it was not reached to a sufficient level. The reason that it is difficult to obtain the adhesion and impact resistance is considered to be that a bonding force between a binder resin in the primer layer and a binder resin in the hard coat layer is not sufficient. To improve the bonding force, it is necessary to increase an amount of functional groups contributing to adhesion of those binder resins. However, where such an approach is taken, there are many cases that crosslinking density of the primer layer and hard coat layer themselves decreases, and mar resistance deteriorates.
Thus, where a primer layer and a hard coat layer are combined in a plastic lens having an antireflective layer comprising an organic thin film, it was difficult to obtain properties responding to all of durability, impact resistance and mar resistance.
The invention has been made in view of the above circumstances.
Objects of the invention are to provide a plastic lens comprising a plastic lens substrate having formed thereon a primer layer, a hard coat layer and an organic antireflective layer, in the order from the surface of the plastic lens substrate, the plastic lens having excellent durability, impact resistance and mar resistance, and a method of producing the plastic lens.